In our Canadian Pat. No. 1,028,552 (and its equivalent U.S. Pat. No. 4,169,090), there is described a process for forming protein isolates which comprises subjecting a protein source material to an aqueous food grade salt solution having a salt concentration of at least about 0.2 ionic strength at a temperature of about 15.degree. to about 35.degree. C. and a pH of about 5.5 to about 6.3, diluting the resulting protein solution to an ionic strength of less than about 0.1 to cause the formation of protein micelles in the aqueous phase, and collecting the protein micelles as an amorphous mass of protein isolate.
The latter process is applicable to the isolation of protein from a wide variety of protein source materials in considerably higher yields than are normally attainable using salting-in procedures. The protein isolate derived by the prior process is substantially undenatured and has functionality not exhibited by the source material nor isoelectric precipitates thereof.
The protein extraction from the source material requires the use of a salt solution having an ionic strength of at least 0.2 to effect protein solubilization and ionic strength values up to 0.8 are generally used, as a result of the high degree of dilution required for protein isolation at higher ionic strength values. Sodium chloride usually is used as the extracting salt but any other convenient food grade salt may be used.
The pH range of 5.5 to 6.3 is selected in the prior process, since the micellar form of the isolate is not obtained in any significant amounts at pH values above 6.3 and protein yields fall significantly at higher values and, while the micellar form of the isolate is obtained at pH values below 5.5 down to about 5.0, phosphorus contamination occurs to an unacceptable degree at pH values below 5.5.